There are many questions that remain in trachoma control. Some of the most important center around the long term use of mass oral antibiotics. In this proposal, we assess whether we can completely eliminate infection with repeated mass treatments, what happens when treatments are discontinued, and whether targeting treatment to high risk groups can prevent the return of infection. Mass antimicrobial administrations have been remarkably successful in reducing the prevalence of the ocular strains of chlamydia that cause trachoma. Repeated distributions progressively lower the prevalence of infection, and in some cases may even result in local elimination. Mass treatments cannot be continued forever, due to concerns about cost and antibiotic resistance. The hope has been that other measures such as latrine construction and hygiene programs would prevent infection from returning. Unfortunately, no non- antibiotic measure has yet demonstrated an effect on infection. Here, we evaluate how infection returns when antibiotics are discontinued, whether infection can be predictably eliminated, and whether infection can be prevented from returning with targeted treatment strategies. This proposal monitors communities from TANA I (U10 EY016214), a NEI-supported collection of cluster- randomized trachoma trials in Ethiopia. In one of the trials, a total of 111 communities will have received repeated mass oral azithromycin distributions over 42 months (final study visit in Fall 2009). These treatments have lowered, and in some cases may have eliminated, infection. Now, we have an unprecedented opportunity to continue to follow these communities, assessing what measures are necessary, if any, to keep infection from returning. It would take years and a great deal of resources to ever again set up these conditions in such a controlled setting. Continued monitoring of these communities will help us to determine the feasibility of control, local elimination, or even eradication. RELEVANCE (provided by the applicant): Trachoma is the leading cause of infectious blindness worldwide. The WHO has initiated a program designed to control infection to a low enough level that resulting blindness will not be a public health concern. Here, we assess whether loftier goals, such as elimination from large areas or even eradication may be feasible, by monitoring treatment in some of the most severely affected communities in the world.